Parmelina pastillifera

Parmelina pastillifera is a species of foliose lichen in the family Parmeliaceae. The species forms greyish rosettes typically 4–8 cm across on nutrient-rich bark, particularly on ash and maple branches, as well as on rocks and tiles in exposed situations. It is readily identified by its characteristic button-like, blue-black outgrowths (isidia) that cover the lobes and often become dense in the centre of the thallus. The lichen occurs in Europe and Great Britain, where it is associated...